There is a legal requirement that vent valves on fuel tanks on highway trucks be closable automatically, so that if a truck is tilted or tipped over, there will be no spillage of fuel through the vent valve. It is also necessary that the vent valve be open during normal operation to allow air into the tank as the fuel therein is decreased, and to allow gas to flow out of the tank if the fuel is being increased in the tank. The requirements are the same when the tank and/or the fuel therein contracts or expands. It is also necessary that there be safety releases against excessive pressure and excessive temperature in a fuel tank.
Government regulations require that all fuel tank vent valves be designed to prevent liquid spillage at any attitude of the fuel tank.
In prior art known to applicant and not cited in the related application, a ball valve, although not bouyant, is seated too easily under the influence of gas flowing out of the tank. This occurred because the ball was too close to the seat and the gas pressure activity on the wall around the ball and on the ball was sufficient to seat the valve when it should have remained open. In addition, the non-bouyant ball valve would not always seat when the valve was vertical or when at less than 30 degrees angle of tilt in the presence of liquid fuel. This was due to respective inaction of two other ball elements in the valve.
The French patent to Bloch, U.S. Pat. No. 853,806 presents a ball container within a body, having a bouyant ball normally positioned vertically above a heavy ball. However, there is not adequate chamber in the body for spinning the ball around a central axis of the body nor are there means to cause it to spin. If the bouyant ball in the French patent were held by the liquid to be near the seat, it could easily be seated by gas flow rather than by the liquid.
A U.S. patent to Seidler, U.S. Pat. No. 2,919,707 does not have provision for rotating a bouyant ball and it appears that it would tend to seat too easily under the influence of gas venting from tank.
U.S. Pat. No. 785,594 to Crispin does not provide a space for rotation of the valve nor does it provide means to cause it to rotate. It appears that the Crispin valve is not meant to prevent spillage on tilting because if it were quickly tilted, the liquid could easily flow out of the orifices directly above the ball where the liquid would be closer to the outlet than the ball.
Other references known to the applicant and more remote from the present invention to those described above are:
______________________________________ U.S. Pat. No. 3,970,098 Boswank et al U.S. Pat. No. 3,662,725 Dragon et al U.S. Pat. No. 1,724,878 Jensen U.S. Pat. No. 2,677,939 Clute U.S. Pat. No. 3,757,987 Marshall U.S. Pat. No. 2,510,098 Geisler U.S. Pat. No. 3,938,692 Crute Great Britain No. 405,385 Price et al German No. 1,150,850 Bopp et al ______________________________________